Search

Context. Monitoring of pulse period variations in accreting binary pulsars is an important tool to study the interaction between the magnetosphere of the neutron star and the accretion disk. While the X-ray flux of the brightest X-ray pulsars have been successfully monitored over many years (e.g. with RXTE/ASM, CGRO/BATSE, Swift/BAT), the possibility to monitor their pulse timing properties continuously has so far been very limited.

We present evidence for the existence of two ~35 day clocks in the Her X-1/HZ Her binary system. ~35 day modulations are observed 1) in the Turn-Oncycles with two on- and two off-states and 2) in the changing shape of the pulse profileswhich re-appears regularly. The two ways of counting the 35 day cycles are generally in synchronization. This synchronization did apparently break down temporarily during the long Anomalous Low(AL3), which Her X-1 experienced in 1999/2000, in the sense that there must have been one extra Turn-Oncycle. Our working hypothesis is that there are two clocks in the system, both with a period of about ~35 days: precession of the accretion disk (the less stable “Turn-Onclock”) and free precession of the neutron star (the more stable “Pulse profileclock”). We suggest that free precession of the neutron star is the master clock and that the precession of the accretion disk is basically synchronized to that of the neutron star through a feedback mechanism in the binary system. However, the Turn-Onclock can slip against its master when the accretion disk has a very low inclination, as is observed to be the case during AL3. We take the apparent correlation between the histories of the Turn-Ons, of the Anomalous Lowsand of the pulse period evolution, with a 5 yr quasi-periodicity, as evidence for strong physical interaction and feedback between the major components in the system. We speculate that the 5 yr (10 yr) period is due either to a corresponding activity cycleof HZ Her or a natural ringingperiod of the physical system of coupled components. The question of whether free precession really exists in neutron stars is very important for understanding matter with supra-nuclear density.

Context. LS 5039 / RX J1826.2-1450 is one of the few High Mass X-ray binary systems from which radio and high energy TeV emission has been observed. Moreover, variability of the TeV emission with orbital period was detected.

Aims. We investigate the spectral and temporal behavior of the high mass X-ray binary Vela X-1 during a phase of high activity, with special focus on the observed giant flares and off states.

In June–September 2006 the Be/X-ray binary EXO 2030+375 experienced the second giant outburst since its discovery. The source was shown to have a complicated pulse-averaged X-ray spectral continuum with possible evidence of cyclotron absorption features. In this paper we present the first pulse-phase resolved analysis of the broad band X-ray spectra of EXO 2030+375 obtained with the INTEGRALobservatory close to the maximum and during the decay phase of the giant outburst. We report a strong variability of the spectrum with pulse phase. Alternative spectral continuum models are discussed. The dependence of the spectral parameters on pulse phase during the maximum of the outburst and the evolution of the pulse profiles with time are qualitatively consistent with the pulsar's emission diagram changing from the fan-beam geometry close to the maximum of the outburst to a combination of pencil and fan beams (of comparable intesities) at the end of the decay phase. Evidence of a cyclotron absorption line around 63 keV at the pulse phase interval preceeding the main peak of the pulse profile is present in the spectrum obtained close to the maximum of the outburst.

Context. The Galactic Plane Scan (GPS) was one of the core observation programmes of the INTEGRALsatellite. The highly variable accreting pulsar OAO 1657-415was frequently observed within the GPS.

Aims. We investigate the X-ray spectral and timing properties of the accreting X-ray pulsar Her X-1 observed with the INTEGRALsatellite in July–August 2005.

Aims.We study the spectral and temporal behavior of the High Mass X-ray Binary A 0535+26 during a “pre-outburst flare” which took place ~ 5 d before the peak of a normal (type I) outburst in August/September 2005. We compare the studied behavior with that observed during the outburst.

We argue that X-ray flaring variability observed in the transient X-ray pulsar A0535+26 is due to low-mode magnetospheric instability. This instability develops at the onset of accretion, in the thin boundary layer between the accretion disk and neutron star magnetosphere. As a result, the matter collected in the boundary layer can rapidly fall onto the NS surface close to the magnetic poles, but not exactly along the field lines by which the stationary accretion proceeds. This explains the shift in cyclotron line energy measured using RXTE data in a pre-outburst spike, with respect to the line energy observed during the main outburst. Furthermore, the instability can account for the difference in pulse profiles, and their energy evolution that is different in the pre-outburst flare and main outburst.

Aims.We study the physics of cyclotron line formation in the high-energy spectra of accreting X-ray pulsars. In particular, we link numerical predictions for the line profiles to results from observational data analysis. Therefore, first we investigate the theoretical predictions and the significance of our model parameters, and second we aim at the development of a model to fit cyclotron lines in observational data.

Aims.In this Letter we present results from INTEGRALand RXTEobservations of the spectral and timing behavior of the High Mass X-ray Binary A 0535+26 during its August/September 2005 normal (type I) outburst with an average flux $F_{(5-100)}\,_{\mathrm{keV}} \sim400$mCrab. The search for cyclotron resonance scattering features (fundamental and harmonic) is one major focus of the paper.

Aims.We present the results of ten years of repeated measurements of the Cyclotron Resonance Scattering Feature (CRSF) in the spectrum of the binary X-ray pulsar Her X-1and report the discovery of a positive correlation of the centroid energy of this absorption feature in pulse phase averaged spectra with source luminosity.

We report on a medium deep XMM-Newton survey of the Marano Field and optical follow-up observations. The mosaicked XMM-Newton pointings in this optical quasar survey field cover 0.6 deg2with a total of 120 ks good observation time. We detected 328 X-ray sources in total. The turnover flux of our sample is $f_{\rm{X}}\sim 5 \times 10^{-15}$erg cm-2s-1in the 0.2-10 keV band. With VLT FORS1 and FORS2 spectroscopy we classified 96 new X-ray counterparts.
The central 0.28 deg2, where detailed optical follow-up observations were performed, contain 170 X-ray sources (detection likelihood $ML>10$), out of which 48 had already been detected by ROSAT. In this region we recover 23 out of 29 optically selected quasars. With a total of 110 classifications in our core sample we reach a completeness of ~65%. About one-third of the XMM-Newton sources are classified as type II AGN with redshifts mostly below 1.0. Furthermore, we detect five high redshift type II AGN ($2.2\le z\le2.8$).
We show that the true redshift distribution of type II AGN remains uncertain, since their lack of emission lines in a wide optical wavelength range hampers their identification in the redshift range $1

Aims.The aim of this paper is to study the evolution of the broadband spectrum of one of the brightest and nearest quasars 3C 273.

Aims.We investigate the X-ray spectral and timing properties of the high mass X-ray binary EXO 2030+375observed during its June–September 2006 giant (type II) outburst.

Aims.We present the results of the INTEGRALmonitoring campaign on the accreting low mass X-ray binary pulsar GX 1+4 performed during the Galactic plane scan of the INTEGRALCore Programme.

Aims.We present an analysis of the accreting X-ray pulsar system 4U 1907+09 based on INTEGRALdata. The main focus of this analysis is a study of the timing behavior of this source. In addition we also show an analysis of the 5–90 keV spectrum.

Aims.We discuss the current X-ray view of the Crab Nebula and Pulsar, summarising our analysis of observations of the source with the EPIC-pn camera on board the XMM-Newtonobservatory. Different modes of EPIC-pn were combined in order to yield a complete scenario of the spectral properties of the Crab resolved in space and time (pulse phase). In addition we give a description of the special EPIC-pn Burst mode and guidance for data reduction in that mode.

We have monitored a type II outburst of the Be/X-ray binary MXB 0656-072in a series of pointed RXTEobservations during October through December 2003. The source spectrum shows a cyclotron resonance scattering feature at $32.8^{+0.5}_{-0.4}$keV, corresponding to a magnetic field strength of $3.67^{+0.06}_{-0.04}\times 10^{12}$G and is stable through the outburst and over the pulsar spin phase. The pulsar, with an average pulse period of $160.4\pm0.4$s, shows a spin-up of 0.45 s over the duration of the outburst. From optical data, the source distance is estimated to be $3.9\pm0.1$kpc and this is used to estimate the X-ray luminosity and a theoretical prediction of the pulsar spin-up during the outburst.

We present the analysis of Rossi X-ray Timing Explorer (RXTE) observations of the turn-on phase of a 35 day cycle of the X-ray binary Her X-1. During the early phases of the turn-on, the energy spectrum is composed of X-rays scattered into the line of sight plus heavily absorbed X-rays. The energy spectra in the 3–17 keV range can be described by a partial covering model, where one of the components is influenced by photoelectric absorption and Thomson scattering in cold material plus an iron emission line at 6.5 keV. In this paper we show the evolution of spectral parameters as well as the evolution of the pulse profile during the turn-on. We describe this evolution using Monte Carlo simulations which self-consistently describe the evolution of the X-ray pulse profile and of the energy spectrum.

We present the analysis of a 100 ks INTEGRAL(3-100 ${\rm keV}$) observation of the transient X-ray pulsar V 0332${+}53$in outburst. The source is pulsating at $P_{\rm Pulse}=4.3751\pm0.0002$s with a clear double pulse from 6 ${\rm keV}$to 60 ${\rm keV}$. The average flux was ~550 mCrab between 20 ${\rm keV}$and 60 ${\rm keV}$. We modeled the broad band continuum from 5 ${\rm keV}$to 100 ${\rm keV}$with a power-law modified by an exponential cut off. We observe three cyclotron lines: the fundamental line at 24.9${^{+0.1}_{-0.1}}$${\rm keV}$, the first harmonic at 50.5${^{+0.1}_{-0.1}}$${\rm keV}$as well as the second harmonic at 71.7${^{+0.7}_{-0.8}}$${\rm keV}$, thus confirming the discovery of the harmonic lines by Coburn et al. (2005) in RXTEdata.

We present results of an observation of the anomalous X-ray pulsar 4U 0142+61 with the EPIC cameras on XMM-Newtonperformed on 2003 January 24. The pulse phase averaged spectrum can be best described by the sum of a black body with a temperature of $kT_{\rm BB} = 0.395(5)\,{\rm keV}$and a power law with photon index $\Gamma=3.62(5)$. The unabsorbed 2-10 keV flux is ${\sim}7.2\times 10^{-11}~{\rm erg}\,{\rm s}^{-1}\,{\rm cm}^{-2}$. No evidence for additional spectral features such as cyclotron lines is present. These results are consistent with those from an earlier Chandraobservation in 2001 May. Phase resolved spectroscopy over the $8.6882(2)$s period (MJD 52 663.93) shows clear variations with pulse phase of Γ, while kTBBshows a small variation of ∼12%. We confirm earlier conclusions by Özel (2001, ApJ, 563, 276) that the emission from AXPs is more like ly to originate from neutron stars with one single and magnetically active region on the neutron star. The significantly different behavior of the soft and hard spectral components with pulse phase, however, cannot be fully reconciled with the present magnetar emission models.

We present pulse phase resolved spectra of the hypergiant high mass X-ray binary GX 301-2. We observed the source in 2001 October with RXTEcontinuously for a total on-source time of almost 200 ks. We model the continuum with both, a heavily absorbed partial covering model and a reflection model. In either case we find that the well known cyclotron resonant scattering feature (CRSF) at ~35 keV is – although present at all pulse phases – strongly variable over the pulse: the line position varies by 25% from 30 keV in the fall of the secondary pulse to 38 keV in the fall of the main pulse where it is deepest. The line variability implies that we are seeing regions of magnetic field strength varying between $3.4\times 10^{12}$G and $4.2\times 10^{12}$G.

Long time scale radio–X-ray correlations in black holes during the hard state have been found in many sources and there seems to emerge a universal underlying relationship which quantitatively describes this behavior. Although it would appear only natural to detect short term emission patterns in the X-ray and – with a certain time lag – in the radio, there has been little evidence for this up to now. The most prominent source for radio–X-ray correlations on short time scales (minutes) so far remains GRS 1915+105 where a single mass ejection could be detected successively in X-ray, IR, and radio wavebands. We analyze a database of more than 4 years of simultaneous radio–X-ray data for Cygnus X-1 from the Ryle Telescope and RXTE PCA/HEXTE. We confirm the existence of a radio–X-ray correlation on long time scales, especially at hard energies. We show that apparent correlations on short time scales in the lightcurves of Cygnus X-1 are most likely the coincidental outcome of white noise statistics. Interpreting this result as a breakdown of radio–X-ray correlations on shorter time scales, this sets a limit to the speed of the jet.

It has been suggested that relativistic jets in quasars may contain a considerable amount of thermal matter. In this paper, we explore the possibility that the Kαline from the thermal matter may appear at tens of keV due to a high Doppler blue-shift. In the jet comoving frame, the energy density of photons originally emitted by the accretion disk and reflected off the broad line region clouds dominates over that of photons of other origin. We discuss the photoionization states of the thermal matter and find that the irons elements are neutral. The high metallicity in quasars enhances the possibility to detect the thermal matter in the relativistic jet in some radio-loud quasars. A highly Doppler blue-shifted Kαline may be detected. We make a prediction for 3C 273, in which the Kαline luminosity might be of the order $3.0\times 10^{44} \;{\rm erg~s^{-1}}$with an equivalent width of 2.4 keV. Such a line could be detected in a future mission.

INTEGRALhas observed the bright quasar 3C 273 on 3 epochs in January 2003 as one of the first observations of the open programme. The observation on January 5 was simultaneous with RXTEand XMM-Newtonobservations. We present here a first analysis of the continuum emission as observed by these 3 satellites in the band from $\simeq$3 keV to $\simeq$500 keV. The continuum spectral energy distribution of 3C 273 was observed to be weak and steep in the high energies during this campaign. We present the actual status of the cross calibrations between the instruments on the three platforms using the calibrations available in June 2003.

We present first results from contemporaneous observations of Cygnus X-1 with INTEGRALand RXTE, made during INTEGRAL's performance verification phase in 2002 November and December. Consistent with earlier results, the $3{-}250$keV data are well described by Comptonization spectra from a Compton corona with a temperature of $kT\sim50{-}90$keV and an optical depth of $\tau\sim 1.0{-}1.3$plus reflection from a cold or mildly ionized slab with a covering factor of $\Omega/2\pi\sim 0.2{-}0.3$. A soft excess below 10 keV, interpreted as emission from the accretion disk, is seen to decrease during the 1.5 months spanned by our observations. Our results indicate a remarkable consistency among the independently calibrated detectors, with the remaining issues being mainly related to the flux calibration of INTEGRAL.

The IBIS telescope is the high angular resolution gamma-ray imager on-board the INTEGRAL Observatory, successfully launched from Baikonur (Kazakhstan) the 17th of October 2002. This medium size ESA project, planned for a 2 year mission with possible extension to 5, is devoted to the observation of the gamma-ray sky in the energy range from 3 keV to 10 MeV (Winkler [CITE]). The IBIS imaging system is based on two independent solid state detector arrays optimised for low ($15{-}1000$keV) and high ($0.175{-}10.0$MeV) energies surrounded by an active VETO System. This high efficiency shield is essential to minimise the background induced by high energy particles in the highly excentric out of van Allen belt orbit. A Tungsten Coded Aperture Mask, 16 mm thick and ~1 squared meter in dimension is the imaging device. The IBIS telescope will serve the scientific community at large providing a unique combination of unprecedented high energy wide field imaging capability coupled with broad band spectroscopy and high resolution timing over the energy range from X to gamma rays. To date the IBIS telescope is working nominally in orbit since more than 9 month.

The INTEGRALScience Data Centre (ISDC) provides the INTEGRALdata and means to analyse them to the scientific community. The ISDC runs a gamma ray burst alert system that provides the position of gamma ray bursts on the sky within seconds to the community. It operates a quick-look analysis of the data within few hours that detects new and unexpected sources as well as it monitors the instruments. The ISDC processes the data through a standard analysis the results of which are provided to the observers together with their data.

We have assembled a sample of 37 radio-loud quasars that have been imaged with the Hubble Space Telescopein order to investigate their black hole masses, accretion rates, and the structure of their accretion disks. The black hole masses were estimated from the luminosities of the host galaxies, and the accretion powers were extrapolated from the emission-line luminosities. The majority of the quasars have masses in the range $M_{\rm BH} \approx 10^8{-}10^9$$M_\odot$. Their accretion rates, $\dot M \approx 0.01{-}1$times the Eddington rate, suggest that most of the objects possess standard optically thick, geometrically thin accretion disks, in some cases perhaps accompanied by an optically thin advection-dominated component. The coexistence of strong radio emission and a standard disk conflicts with recent models for jet formation. We discuss modifications of the standard model that can resolve this discrepancy. We find there is a strong correlation between the accretion rate and the extended radio luminosity. This lends support to the idea that the extended radio emission is somehow linked to the accretion disk. Lastly, we combine the present sample of radio-loud quasars with the sample of BL Lac objects studied by Wang et al. (2002) to reevaluate the unification picture for radio-loud active galactic nuclei. Consistent with current ideas for the unification of radio-loud sources, we find that flat-spectrum radio quasars and FR II radio galaxies indeed seem to belong to the same population, as do BL Lac objects and FR I radio galaxies on the opposite end of the luminosity spectrum. However, some members of the low frequency-peaked BL Lac objects may be more closely associated with FR II rather than FR I radio galaxies. We describe how the various subclasses of radio-loud sources can be viewed as a continuous sequence of varying accretion rate.

We present the long term evolution of the timing properties of the black hole candidate Cygnus X–1in the 0.002–128 Hz frequency range as monitored from 1998 to 2001 with the Rossi X-ray Timing Explorer (RXTE). For most of this period the source was in its hard state. The power spectral density (PSD) is well modeled as the sum of four Lorentzians, which describe distinct broad noise components. Before 1998 July, Cyg X–1 was in a “quiet” hard state characterized primarily by the first three of these broad Lorentzians being dominant. Around 1998 May, this behavior changed: the total fractional rms amplitude decreased, the peak frequencies of the Lorentzians increased, the average time lag slightly increased, and the X-ray spectrum softened. The change in the timing parameters is mainly due to a strong decrease in the amplitude of the third Lorentzian. Since this event, an unusually large number of X-ray flares have been observed, which we classify as “failed state transitions”. During these failed state transitions, the X-ray power spectrum changes to that of the intermediate state. Modeling this PSD with the four Lorentzians, we find that the first Lorentzian component is suppressed relative to the second and third Lorentzian during the state transitions. We also confirm our previous conclusion that the frequency-dependent time lags increase significantly in the 3.2–10 Hz band during these transitions. We confirm the interpretation of the flares as failed state transitions with observations from the 2001 January and 2001 October soft states. Both the behavior of the PSD and the X-ray lag suggest that some or all of the Lorentzian components are associated with the accretion disk corona responsible for the hard state spectrum. We discuss the physical interpretation of our results.

The magnetic Cataclysmic Variable (mCV) V1432 Aql(RX J1940.1–1025) belongs to the four-member subclass of near-synchronous polars with a slight non-synchronism (<2%) between the spin period of the white dwarf and the binary period. In these systems the accretion geometry changes periodically with phase of the beat cycle. We present the application of a dipole accretion model for near-synchronous systems developed by Geckeler & Staubert (1997a) to extended optical and X-ray data. We detect a significant secular change of the white dwarf spin period in V1432 Aqlof ${\rm d}P_{\rm spin}/{\rm d}t=-5.4^{+3.7}_{-3.2}\times 10^{-9}$s/s from the optical data set alone. This corresponds to a synchronization time scale $\tau_{\rm sync}=199^{+441}_{-75}$yr, comparable to the time scale of 170 yr for V1500 Cyg. The synchronization time scale in V1432 Aqlis in excellent agreement with the theoretical prediction from the dominating magnetic torque in near-synchronous systems. We also present period analyses of optical CCD photometry and RXTE X-ray data, which argue against the existence of a 4000 s period and an interpretation of V1432 Aqlas an intermediate polar. The dipole accretion model also allows us to constrain the relevant parameters of the accretion geometry in this system: the optical data allow an estimate of the dimensionless parameter $({R}_{\rm t0}'/{R}_{\rm wd})^{1/2}\sin{\beta}=3.6_{-1.1}^{+2.7}$, with a lower limit for the threading radius of ${R}_{\rm t0}'>10\,{R}_{\rm wd}$(68% confidence).

We present pulse phase-resolved X-ray spectra of the high mass X-ray binary Vela X-1 using the Rossi X-ray Timing Explorer. We observed Vela X-1 in 1998 and 2000 with a total observation time of ~90 ksec. We find an absorption feature at $23.3^{+1.3}_{-0.6}~ke\kern -0.09em V$in the main pulse, that we interpret as the fundamental cyclotron resonant scattering feature (CRSF). The feature is deepest in the rise of the main pulse where it has a width of $7.6^{+4.4}_{-2.2}~ke\kern -0.09em V$and an optical depth of $0.33^{+0.06}_{-0.13}$. This CRSF is also clearly detected in the secondary pulse, but it is far less significant or undetected during the pulse minima. We conclude that the well known CRSF at $50.9^{+0.6}_{-0.7}~ke\kern -0.09em V$, which is clearly visible even in phase-averaged spectra, is the first harmonic and notthe fundamental. Thus we infer a magnetic field strength of $B=2.6\times 10^{12}$G.

We report on an observation of the anomalous X–ray pulsar 1E 1048.1–5937 performed with the XMM-Newtonsatellite. The phase averaged spectrum of 1E 1048.1–5937 is well described by the sum of a power law with photon index ~2.9 and a blackbody with temperature ~0.6 keV, without evidence for significant absorption or emission lines. The above spectral parameters do not vary during the phases corresponding to the broad pulse, while the off pulse emission shows a different spectrum characterized by a soft excess at energies below ~1.5 keV. The XMM-Newtonobservation and a re-analysis of archival BeppoSAX data show that the spectral parameters and flux of 1E 1048.1–5937 did not change significantly during observations spanning the last four years. All the data are consistent with a 2–10 keV luminosity varying in the range ~(5–7)$\times$1033erg s-1(for a distance of 3 kpc).

We report on the analysis from ~110 ks of X-ray observations of Centaurus A carried out with the Proportional Counter Array (PCA) and the High Energy X-ray Timing Experiment (HEXTE) instruments on Rossi X-ray Timing Explorer (RXTE) during three monitoring campaigns over the last 4 years (10 ks in 1996, 74 ks in 1998, and 25 ks in 2000). The joint PCA/HEXTE X-ray spectrum can be well described by a heavily absorbed power law with photon index 1.8 and a narrow iron line due to fluorescence of cold matter. The measured column depth decreased by about $30\%$between 1996 and 2000, while the detected 2-10 keV continuum flux remained constant between 1996 and 1998, but increased by $60 \%$in 2000. Since in all three observations the iron line flux did not vary, a corresponding decrease in equivalent width was noted. No appreciable evidence for a reflection continuum in the spectrum was detected. We present the interpretation of the iron line strength through Monte Carlo computations of various geometries. No significant temporal variability was found in Cen A at time scales from days to tens of minutes.

We present the XMM-Newtonfirst light image, taken in January 2000 with the EPIC pn camera during the instrument's commissioning phase, when XMM-Newtonwas pointing towards the Large Magellanic Cloud (LMC). The field is rich in different kinds of X-ray sources: point sources, supernova remnants (SNRs) and diffuse X-ray emission from LMCinterstellar gas. The observations are of unprecedented sensitivity, reaching a few 10$\sp{32}$erg/s for point sources in the LMC. We describe how these data sets were analysed and discuss some of the spectroscopic results. For the SNR N157Bthe power law spectrum is clearly steeper than previously determined from ROSAT and ASCA data. The existence of a significant thermal component is evident and suggests that N157Bis not a Crab-like but a composite SNR. Most puzzling is the spectrum of the LMChot interstellar medium, which indicates a significant overabundance of Ne and Mg of a few times solar.

The European Photon Imaging Camera (EPIC) consortium has provided the focal plane instruments for the three X-ray mirror systems on XMM-Newton. Two cameras with a reflecting grating spectrometer in the optical path are equipped with MOS type CCDs as focal plane detectors (Turner [CITE]), the telescope with the full photon flux operates the novel pn-CCD as an imaging X-ray spectrometer. The pn-CCD camera system was developed under the leadership of the Max-Planck-Institut für extraterrestrische Physik (MPE), Garching. The concept of the pn-CCD is described as well as the different operational modes of the camera system. The electrical, mechanical and thermal design of the focal plane and camera is briefly treated. The in-orbit performance is described in terms of energy resolution, quantum efficiency, time resolution, long term stability and charged particle background. Special emphasis is given to the radiation hardening of the devices and the measured and expected degradation due to radiation damage of ionizing particles in the first 9 months of in orbit operation.

Aims. We analyze 1050?ks of INTEGRAL data of the high mass X-ray binary pulsar 1E?1145.1-6141 to study its properties over a long time baseline, from June 2003 to June 2004, with wide spectral coverage. Methods. We study three high luminosity episodes, two of them at the system apoastron, three brightening with lower intensity, two at the periastron, and one extended period of intermediate luminosity spanning one orbital cycle. We perform a timing analysis to determine the pulse period and pulse profiles at different energy ranges. We also analyze the broad band phase averaged spectrum of different luminosity states and perform phase resolved spectroscopy for the first flare. Results. From the timing analysis, we find a pulse period of ~297?s around MJD?53?000 with a significant scatter around the mean value. From the spectral analysis we find that the source emission can be described by an absorbed bremsstrahlung model in which the electron temperature varies between ~25 and ~37?keV, without any correlation with luminosity, and the intrinsic absorbing column is constantly of the order of 1023cm-2. Phase resolved spectral analysis reveals a different temperature of the plasma in the ascending and descending edges of the pulse during the first flare. This justifies the pulse maximum shift by ~0.4 phase units between 20 and 100?keV observed in the pulse profiles. Conclusions. The comparison with the previous period measurements reveals that the source is currently spinning down, in contrast to the long term secular trend observed so far, indicating that at least a temporary accretion disk is formed. The study of the spectral property variations with respect to time and spin phase suggests the presence of two emitting components at different temperatures whose relative intensity varies with time.

We present evidence for the existence of two ~35?day clocks in the Her?X-1/HZ?Her binary system. ~35?day modulations are observed 1) in the Turn-On cycles with two on- and two off-states and 2) in the changing shape of the pulse profiles which re-appears regularly. The two ways of counting the 35?day cycles are generally in synchronization. This synchronization did apparently break down temporarily during the long Anomalous Low (AL3), which Her X-1 experienced in 1999/2000, in the sense that there must have been one extra Turn-On cycle. Our working hypothesis is that there are two clocks in the system, both with a period of about ~35?days: precession of the accretion disk (the less stable ?Turn-On clock?) and free precession of the neutron star (the more stable ?Pulse profile clock?). We suggest that free precession of the neutron star is the master clock and that the precession of the accretion disk is basically synchronized to that of the neutron star through a feedback mechanism in the binary system. However, the Turn-On clock can slip against its master when the accretion disk has a very low inclination, as is observed to be the case during AL3. We take the apparent correlation between the histories of the Turn-Ons, of the Anomalous Lows and of the pulse period evolution, with a 5?yr quasi-periodicity, as evidence for strong physical interaction and feedback between the major components in the system. We speculate that the 5?yr (10?yr) period is due either to a corresponding activity cycle of HZ?Her or a natural ringing period of the physical system of coupled components. The question of whether free precession really exists in neutron stars is very important for understanding matter with supra-nuclear density.

Context. LS?5039?/?RX?J1826.2-1450 is one of the few High Mass X-ray binary systems from which radio and high energy TeV emission has been observed. Moreover, variability of the TeV emission with orbital period was detected.Aims. We investigate the hard X-ray (25-200?keV) spectral and timing properties of the source with the monitoring IBIS/ISGRI instrument on-board the INTEGRAL satellite. Methods. We present the analysis of INTEGRAL observations for a total of about 3?Msec exposure time, including both public data and data from the Key Programme. We search for flux and spectral variability related to the orbital phase.Results. The source is observed to emit from 25 up to 200?keV and the emission is concentrated around inferior conjunction. Orbital variability in the hard X-ray band is detected and established to be in phase with the orbitally modulated TeV emission observed with HESS. For this energy range we determine an average flux for the inferior conjunction phase interval of (3.54 ?2.30) ?10-11?erg?cm-2?s-1, and a flux upper limit for the superior conjunction phase interval of 1.45 ?10-11?erg?cm-2?s-1(90%?conf. level respectively). The spectrum for the inferior conjunction phase interval follows a power law with an index ?= 2.0+0.2-0.2(90%?conf. level).

We present an update of the orbital ephemeris of the binary X-ray pulsar Her X-1 and determine an improved value for the rate of orbital decay. In addition, we report the first measurement of the orbital eccentricity. We analyzed pulse timing data of Her X-1 from X-ray observations by RXTE (Rossi X-Ray Timing Explorer) and INTEGRAL over the period 1996?2007. Accurate pulse arrival times were determined from solar system bary-centered photon arrival times by generating pulse profiles averaged over appropriately short integration times. Applying pulse phase connection techniques, it was possible to determine sufficiently accurate local ephemeris data for seven observation periods distributed over 12 years. Combining the new local T?/2values with historical values from the literature we update the orbital ephemeris of Her X-1 to T?/2= MJD 46?359.871940(6) and Porb= 1.700167590(2)?d and measure a continuous change of the orbital period of dPorb/dt = -(4.85 ?0.13) ?10-11ss-1. For the first time, a value for the eccentricity of the orbit of Her?X-1 has been measured: ?= (4.2 ?0.8) ?10-4.